Mixed day for Americans at Wimbledon

Serena Williams of the United States reacts after scoring a point against Caroline Garcia of France during their Women's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Alastair Grant)

Serena Williams of the United States returns to Caroline Garcia of France during their Women's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Alastair Grant)

Serena Williams of the United States serves to Caroline Garcia of France during their Women's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Alastair Grant)

Serena Williams of the United States reacts during her Women's second round singles match against Caroline Garcia of France at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Alastair Grant)

Serena Williams of the United States serves to Caroline Garcia of France during their Women's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Alastair Grant)

Novak Djokovic of Serbia jumps during his Men's second round singles match against Bobby Reynolds of the United States at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Kirsty Wigglesworth)

Novak Djokovic of Serbia plays a return to Bobby Reynolds of the United States during their Men's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Kirsty Wigglesworth)

Novak Djokovic of Serbia plays a return to Bobby Reynolds of the United States during their Men's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Kirsty Wigglesworth)

Novak Djokovic of Serbia reacts after defeating Bobby Reynolds of the United States in their Men's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Kirsty Wigglesworth)

Madison Keys of the United States returns to Mona Barthel of Germany during their Women's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Sang Tan)

Madison Keys of the United States returns to Mona Barthel of Germany during their Women's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Sang Tan)

Denis Kudla of the United States reacts as he plays Ivan Dodig of Croatia in their Men's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Sang Tan)

James Blake of the United States volleys a return to Bernard Tomic of Australia during their Men's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Sang Tan)

Bobby Reynolds of the United States wipes himself with a towel as he faces Novak Djokovic of Serbia in their Men's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Kirsty Wigglesworth)

Bernard Tomic of Australia reacts as James Blake of the United States contests a line call during their Men's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Sang Tan)

Bernard Tomic of Australia reacts as James Blake of the United States contests a line call during their Men's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Sang Tan)

Juan Martin Del Potro of Argentina reacts after scoring a point against Jesse Levine of Canada during their Men's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Kirsty Wigglesworth)

Andy Murray of Britain reacts during his Men's second round singles match against Lu Yen-Hsun of Taiwan at the All England Lawn Tennis Championships in Wimbledon, London, Wednesday, June 26, 2013. (AP Photo/Sang Tan)

Li Na of China returns to Simona Halep of Romania during their Women's second round singles match at the All England Lawn Tennis Championships in Wimbledon, London, Thursday, June 27, 2013. (AP Photo/Anja Niedringhaus)